1. Field of the Invention
The present invention relates to electrical contact materials, and more particularly to an electrical contact material of silver matrix containing no cadmium-composite, and having the features of high hardness, high wear resistance and low contact resistance, while maintaining a better arc erosion resistance.
2. Description of the Related Art
At present, electrical contact material is used extensively in the different areas that require an electrical contact, such as communication transmission, system or power output control, electronic instrument connection, and computer peripherals, etc. In general, a phenomenon of producing an electric discharge usually occurs when an electric connector or a relay is turned on/off, since the distance between two electric contact is very small when they are about to contact with or separate from one another. Under an environment with a high electric field distribution, current between the two electric contacts produces such electric discharge phenomenon, which further causes the formation of an electric arc.
In general, a mass transfer of the materials usually occurs between two electrical contacts during an arc erosion process, and a protrusion or a recess is formed on a surface of the electrical contact, or a rough source is formed on the surface of the electrical contact after a metal is melted and solidified in the arc erosion, and other contaminations or damages caused by the aforementioned phenomena will destroy the smooth surface of the original electrical contact and increase the contact resistance, which will further affect the working performance of the electrical contact.
In practical applications, manufacturers of the related industry have been using platinum as a matrix material, but platinum incurs a high cost, and it is gradually replaced by copper. Although copper has the advantages of high electrical and thermal conductivities and a low cost, yet oxides may be fowled easily on the surface of copper, so that a silver matrix having the same advantages of copper is introduced and used as a matrix material. Although silver can resist oxidation, silver has the disadvantages of a lower strength, a lower wear resistance and a severer arc erosion phenomenon which are unfavorable for a long time use as an electrical contact material. At a later stage, a more economic CdO/Ag contact material was developed, and such contact material has the advantages of a high electrical conductivity, a high thermal conductivity, and a good erosion resistance, such that the CdO/Ag contact material can be used for conducting a larger current and applied to a heavy-duty or very large switch or relay. However, Cd is highly toxic, and the European Commission has officially banned electronic products using a highly toxic substance such as Cd and Pb through the WEEE and RoHS directives.
With reference to FIGS. 1A and 1B for schematic views showing the surface of a connector with a conventional AuCo electrical contact material gone through an arc erosion test for 500 times, the surface of the conventional electrical contact material is seriously damaged after the material has gone through the arc erosion test for 500 times, and thus resulting in a short lifespan and a poor performance of the electric contact material.
It is an important subject for manufacturers of the related industry to provide an electrical contact material in compliance with the international specification of a toxic-free material and having the advantages of high electrical conductivity, good erosion resistance, and high hardness to meet the aforementioned requirements.